The present invention relates generally to communications systems, and in particular to an improved cable communications system. Still more particularly, the present invention relates to a method and apparatus for shifting communications units within a cable communications system into various states of activity.
In a cable communications system using hybrid fiber coaxial cable, large numbers of subscriber units derive bias voltage, current or AC/DC supply power from network power supplies. Such cable communications systems use time division multiplexing to take advantage of trunking efficiencies. In this type of system, the infrastructure is not capable of servicing all subscriber units simultaneously Typically, subscriber units operate either in an active state or a standby state, also called a sleep state. In the active state, a subscriber unit is in the highest power consumption state in which the receiver and transmitter of the subscriber unit are powered up. In the standby or sleep state, a subscriber unit is in its lowest power consumption state. A subscriber unit in an active state can consume ten times more power than a subscriber unit in the sleep state.
Subscriber units are required to register on a cable communications system after reset to receive network wide system parameters. Registration with the cable communications system requires the subscriber unit to enter the active state. During periods of network power supply outages within the cable communications system infrastructure, all subscriber units are reset. When network power supplies are restored, all subscriber units simultaneously enter the active state for registration. When large numbers of subscriber units enter the active state simultaneously, a peak power load occurs on the power supply in the cable communications system and congestion occurs, effectively blocking subscriber unit access. This blocking increases the time required to register a subscriber unit. Additionally, peak power loads can trip protection circuits within the cable communications system, causing the subscriber unit to reset again. The power up registration attempt followed by power supply overload protection circuits being tripped can cause the cable communications system to become unstable.
Therefore, it would be desirable to have an improved method and apparatus for registering subscriber units in a cable communications system.